A conventional optical fiber disclosed in U.S. Pat. No. 6,941,047 contains a glass piece on which multiple filter films 200a-200d are attached, and the multiple filter films correspond to multiple prisms 230 respectively so that after lights enter into the glass piece from external environment, they are reflected by the multiple filter films to penetrate out of the multiple prisms. Because a gap is defined among the multiple prisms and filter films, the lights lose as passing through multiple mediums. Furthermore, angles of the multiple prisms are fixed respectively, so the lights of different wavelengths have various refractions when passing through the multiple prisms, thus increasing energy loss.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.